Atrial capture verification

ABSTRACT

Methods and systems for classifying cardiac responses to pacing stimulation and/or preventing retrograde cardiac conduction are described. Following delivery of a pacing pulse to an atrium of the patient&#39;s heart during a cardiac cycle, the system senses in the atrium for a retrograde P-wave. The system classifies the atrial response to the pacing pulse based on detection of the retrograde P-wave. The system may also sense for an atrial evoked response and utilize the atrial evoked response in classifying the cardiac pacing response.

RELATED PATENT DOCUMENTS

This is a divisional of Ser. No. 11/012,433, filed Dec. 15, 2004, nowU.S. Pat. No. 7,587,240, to which Applicant claims priority under 35U.S.C. §120, and which is incorporated herein by reference. This patentapplication is related to commonly owned U.S. patent applicationidentified by Ser. No. 11/012,692 filed on Dec. 15, 2004, now publishedas U.S. Patent Publication 20060129199, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates generally to implantable medical devicesand, more particularly, to verifying atrial capture following deliveryof a pacing pulse.

BACKGROUND OF THE INVENTION

When functioning normally, the heart produces rhythmic contractions andis capable of efficiently pumping blood throughout the body. However,due to disease or injury, the heart rhythm may become irregularresulting in diminished pumping efficiency.

Arrhythmia is a general term used to describe heart rhythmirregularities arising from a variety of physical conditions and diseaseprocesses. Cardiac rhythm management systems, such as implantablepacemakers and cardiac defibrillators, have been used as an effectivetreatment for patients with serious arrhythmias. These systems typicallyinclude circuitry to sense electrical signals from the heart and a pulsegenerator for delivering electrical stimulation pulses to the heart.Leads extending into the patient's heart are connected to electrodesthat contact the myocardium for sensing the heart's electrical signalsand for delivering stimulation pulses to the heart in accordance withvarious therapies.

Cardiac rhythm management systems operate to stimulate the heart tissueadjacent to the electrodes to produce a contraction of the tissue.Pacemakers are cardiac rhythm management systems that deliver a seriesof low energy pace pulses timed to assist the heart in producing acontractile rhythm that maintains cardiac pumping efficiency. Pacepulses may be intermittent or continuous, depending on the needs of thepatient. There exist a number of categories of pacemaker devices, withvarious modes for sensing and pacing one or more heart chambers.

When a pace pulse produces a contraction in the heart tissue, theelectrical cardiac signal following the contraction is denoted thecaptured response (CR). The captured response may include an electricalsignal, denoted the evoked response signal, associated with the heartcontraction, along with a superimposed signal associated with residualpost pace polarization at the electrode-tissue interface. The magnitudeof the residual post pace polarization signal, or pacing artifact, maybe affected by a variety of factors including lead polarization,after-potential from the pace pulse, lead impedance, patient impedance,pace pulse width, and pace pulse amplitude, for example.

A pace pulse must exceed a minimum energy value, or capture threshold,to produce a contraction. It is desirable for a pace pulse to havesufficient energy to stimulate capture of the heart without expendingenergy significantly in excess of the capture threshold. Thus, accuratedetermination of the capture threshold may be required for efficientpace energy management. If the pace pulse energy is too low, the pacepulses may not reliably produce a contractile response in the heart andmay result in ineffective pacing. If the pace pulse energy is too high,the patient may experience discomfort and the battery life of the devicewill be shorter.

Capture detection allows the cardiac rhythm management system to adjustthe energy level of pace pulses to correspond to the optimum energyexpenditure that reliably produces a contraction. Further, capturedetection allows the cardiac rhythm management system to initiate aback-up pulse at a higher energy level whenever a pace pulse does notproduce a contraction.

Retrograde conduction may occur, for example, when a depolarization waveinitiated in a ventricle by a pacing pulse or intrinsic activationtravels back to the atrium producing a retrograde P-wave. RetrogradeP-waves may inhibit effective atrial pacing. A pacing pulse delivered tothe atrium will not result in capture if the atrial tissue is refractorydue to a retrograde P-wave. Further, retrograde conduction to the atriummay cause pacemaker mediated tachycardia.

There is a need in the technology for methods and systems that reliablydetermine if a pacing pulse captures an atrium. There is a further needfor methods and systems that provide atrial retrograde management. Thepresent invention fulfills these and other needs.

SUMMARY OF THE INVENTION

The present invention is directed to methods and systems for classifyingcardiac responses to atrial pacing. One embodiment of the inventioninvolves a method for classifying a cardiac response to pacing. A pacingpulse is delivered to an atrium during a cardiac cycle. A pacing pulseis delivered to an atrium if an intrinsic ventricular activation is notsensed during the cardiac cycle. If, responsive to the ventricularpacing pulse or the intrinsic ventricular activation, a retrogradeP-wave is detected in the atrium, the cardiac response to the atrialpacing pulse is classified as a non-captured response.

According to one aspect of the invention, if an atrial evoked responseis not detected and a retrograde P-wave responsive to the ventricularpacing pulse or intrinsic activation is detected, the cardiac responseto the atrial pacing pulse is classified as a non-captured response.

In yet another embodiment of the invention, a cardiac system includes aplurality of implantable electrodes configured for one or more ofsensing a cardiac signal and delivering cardiac pacing pulses to apatient. A housing is configured for implantation in the patient. Acontroller is provided in the housing and is coupled to the plurality ofimplantable electrodes. The controller is configured to deliver a pacingpulse to an atrium of the patient's heart during a cardiac cycle, sensefor an intrinsic activation of a ventricle during the cardiac cycle,deliver a pacing pulse to the ventricle if the intrinsic activation isnot sensed during the cardiac cycle. The cardiac system senses in theatrium for a retrograde P-wave in response to the ventricular pacingpulse or the intrinsic activation. The cardiac response is classified asa non-captured response if the retrograde P-wave is detected.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a graph illustrating a method of confirming atrial loss ofcapture in accordance with embodiments of the invention;

FIG. 1B is a flowchart illustrating a method of atrial captureverification in accordance with embodiments of the invention;

FIG. 1C is a flowchart illustrating a method of determining a cardiacresponse to a pacing pulse using both an atrial evoked response andretrograde P-wave detection in accordance with embodiments of theinvention

FIG. 1D is a flowchart illustrating a method of retrograde management inaccordance with embodiments of the invention;

FIG. 1E is a flowchart illustrating in more detail a retrogradeconduction management method in accordance with embodiments of theinvention;

FIGS. 1F and 1G illustrate the operation of a retrograde managementmethod in accordance with embodiments of the invention;

FIG. 2 illustrates an implantable cardiac rhythm management system thatmay be used in connection with atrial capture verification methodologiesin accordance with embodiments of the invention;

FIG. 3 is a block diagram of an implantable medical device that may beused to verify atrial capture and manage atrial retrograde conduction inaccordance with embodiments of the invention;

FIG. 4A is a flowchart of a method of capture detection based onretrograde conduction in accordance with the present invention;

FIG. 4B is a flowchart of a method of retrograde management inaccordance with the present invention; and

FIG. 4C is a flowchart of a method of capture detection and retrogrademanagement in accordance with the present invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail below. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents, and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In the following description of the illustrated embodiments, referencesare made to the accompanying drawings forming a part hereof, and inwhich are shown, by way of illustration, various embodiments by whichthe invention may be practiced. It is to be understood that otherembodiments may be utilized, and structural and functional changes maybe made without departing from the scope of the present invention.

After delivery of a pacing pulse to a heart chamber, various cardiacresponses to the pacing pulse are possible. In one scenario, the pacingpulse may generate a propagating wavefront of depolarization resultingin a contraction of the heart chamber. In this scenario, the pacingpulse is said to have captured the heart chamber. Capture of the heartchamber may occur if the pacing pulse has sufficient energy and isdelivered during a non-refractory period. If the pacing pulse does notproduce contraction of the chamber, the cardiac response is referred toas non-capture or loss of capture. Non-capture may occur, for example,if the pacing pulse energy is too low, and/or if the pacing pulse isdelivered during a refractory period of the cardiac tissue.

By way of example, the processes of the present invention may be used incapture threshold testing to determine the optimal energy for pacing.The minimum pacing energy that produces capture is referred to as thecapture threshold. It is desirable for a pace pulse to have sufficientenergy to capture the heart without expending excess energy above thecapture threshold. Thus, accurate determination of the capture thresholdmay be desirable for efficient pacing.

Those skilled in the art will appreciate that reference to a capturethreshold testing procedure indicates a method of determining thecapture threshold in one or more of the left atrium, right atrium, leftventricle, and right ventricle. In such a procedure, the pacemaker,automatically or upon command, initiates a search for the capturethreshold of the selected heart chamber. The capture threshold isdefined as the lowest pacing energy that consistently captures theheart.

In one example of an automatic capture threshold procedure, thepacemaker delivers a sequence of pacing pulses to the heart and detectsthe cardiac responses to the pace pulses. The energy of the pacingpulses may be decreased in discrete steps until a predetermined numberof loss-of-capture responses occur. The pacemaker may increase thestimulation energy in discrete steps until a predetermined number ofcapture responses occur to confirm the capture threshold. A capturethreshold test may be performed using cardiac response classificationmethods of the present invention.

Other procedures for implementing capture threshold testing may beutilized. In one example, the pacing energy may be increased in discretesteps until capture is detected. In another example, the pacing energymay be adjusted according to a binomial search pattern.

Capture threshold determination is distinguishable from automaticcapture detection, a procedure that typically occurs on a beat-by-beatbasis during pacing. Automatic capture detection verifies that adelivered pace pulse results in a captured response. When a capturedresponse is not detected following a pace pulse, the pacemaker maydeliver a back up safety pace to ensure consistent pacing. The back uppace may be delivered, for example, about 70-80 ms after the initialpace pulse. If a predetermined number of pace pulses delivered duringnormal pacing do not produce a captured response, the pacemaker mayinitiate a capture threshold test to determine the capture threshold.Alternatively, if a predetermined number of pacing pulses do not producea captured response, the pacemaker may adjust the pacing energy for thenext pacing pulse. Atrial capture verification and atrial retrogrademanagement may be implemented using processes of the present invention.

Embodiments of the invention are directed to methods and systems fordetermining if an atrial pacing pulse captures or fails to capture theatrium. Loss of capture determination may be based on detection of aventricular depolarization wave that travels back to theatrium—retrograde conduction. This retrograde depolarization wave may besensed and used in capture verification processes of the presentinvention.

When a ventricular depolarization occurs, either intrinsically, or as aresult of a ventricular pace, the depolarization wavefront may traveltowards the atrium if the atrial tissue is not in its refractory period.If the myocardial tissue of the atrium is not refractory (i.e., if therewas no intrinsic P-wave or the atrium was not captured by an atrialpacing pulse preceding the ventricular depolarization), then thewavefront initiated by the ventricular depolarization is more likely tobe retrogradely conducted and sensed in the atrium as a retrogradeP-wave. Thus, sensing a retrograde P-wave indicates that the atrialpacing pulse did not capture the atrium.

Further embodiments of the invention involve approaches for avoiding ormanaging atrial retrograde conduction when an atrial pacing pulse doesnot capture the atrium. According to some embodiments, a back up pacecan be delivered to the atrium following loss of capture event. Backuppacing is delivered at a relatively high energy level to ensure captureand thus prevents retrograde conduction to the atrium.

Other retrograde management approaches described herein involve delayingthe next scheduled pace if a retrograde P-wave is detected. Followingdetection of the retrograde P-wave, the next scheduled atrial pace isdelayed until expiration of an effective atrial refractory period.Delaying the next scheduled pace allows the myocardium to recover fromits refractory due to the retrograde conduction before the next pacingpulse is delivered.

FIG. 1A is a graph illustrating a method of confirming atrial loss ofcapture in accordance with embodiments of the invention. This method maybe used, for example, in a dual chamber device. When atrial capture islost, AV synchrony may be disrupted, and a ventricular pulse may occurafter the failed atrial pulse when an atrioventricular delay expires.Because the ventricle is activated before the atrium, the excitation maytravel up to activate the atrium as retrograde conduction.

In the graph of FIG. 1A, an atrial pacing pulse 110 that captures theatrium is followed by an evoked atrial response (AER) 114, and anintrinsic ventricular response 112, which is a QRS complex. A postventricular atrial refractory period (PVARP) 140 is illustratedfollowing the intrinsic ventricular response 112. This is an atrialpaced heartbeat with intrinsic ventricular response.

The next heartbeat begins with an atrial pacing pulse 120 that capturedthe atrium. The atrial pacing pulse 120 is followed by an atrial evokedresponse 124. A ventricular pacing pulse 125 is delivered which capturesthe ventricle producing a ventricular evoked response 122. Theventricular evoked response shows a widened QRS complex relative to theintrinsic ventricular response 112. A PVARP 140 is illustrated followingthe ventricular pacing pulse 125.

The final heartbeat of FIG. 1A illustrates an atrial retrogradeconduction. The atrial pacing pulse 130 does not capture the atrium,thus an atrial evoked response is not sensed. The atrial pacing pulse130 is followed, after an atrioventricular delay, by a ventricularpacing pulse 135, and a ventricular evoked response 132, showing awidened QRS complex relative to the intrinsic ventricular response 112.A PVARP 140 is illustrated following the ventricular pulse 135. Anatrial P-wave 134 is illustrated within the PVARP 140 following theventricular pulse 135. The retrograde P-wave is produced by adepolarization wavefront initiated by the ventricular pulse 135 andconducted to the atrium. If retrograde conduction occurs in closeproximity to a scheduled atrial pacing pulse, capture of the atrium maynot occur regardless of the pulse being greater than a capturethreshold.

The atrial evoked response and/or retrograde P-wave occurring during acardiac cycle may be utilized both for atrial capture verificationand/or atrial retrograde management. FIGS. 1B-1C are flowchartsillustrating atrial capture verification in accordance with embodimentsof the invention.

The flowchart of FIG. 1B illustrates capture verification based on asensed retrograde P-wave. A pacing pulse is delivered 101 to an atriumduring a cardiac cycle. The system senses for 102 an intrinsicactivation of a ventricle during the cardiac cycle. If intrinsicventricular activation is not sensed 103, then a pacing pulse isdelivered 104 to the ventricle.

The system senses for 105 a retrograde P-wave responsive to theintrinsic ventricular activation or the ventricular pace. If theretrograde P-wave is detected 106, then atrial non-capture is morelikely 107. If the retrograde P-wave is not detected 106, then thesystem may classify 109 the cardiac response to the atrial pace as acaptured response.

The flowchart of FIG. 1C illustrates a method of determining a cardiacresponse to a pacing pulse using both an atrial evoked response andretrograde P-wave detection. Use of both the atrial evoked response andretrograde P-wave detection enhances the accuracy of captureverification processes. An atrial pacing pulse is delivered 150. Thesystem senses for 151 an atrial evoked response following the atrialpacing. The system senses for 152 an intrinsic ventriculardepolarization. A pacing pulse is delivered 154 to the ventricle if anintrinsic activation of the ventricle is not detected 153.

Following delivery of the ventricular pace or the intrinsic ventriculardepolarization, the system senses in the atrium for 155 a retrogradeP-wave. The cardiac response to the atrial pacing pulse is classified156 as a non-captured response if the retrograde P-wave is detected andthe atrial evoked response is not detected.

As previously discussed non-capture of the atrium may result in a seriesof retrograde P-waves which are undesirable for effective pacing.Various embodiments involve the providing retrograde management ifatrial non-capture is detected. The flowchart of FIG. 1D illustrates amethod of retrograde management in accordance with embodiments of theinvention. A pacing pulse is delivered 161 to an atrium during a cardiaccycle. If intrinsic activation of the ventricle is not sensed 162 duringthe cardiac cycle, then a pacing pulse is delivered 163 to theventricle. The depolarization wavefront initiated by the intrinsicventricular activation or the ventricular pacing pulse may causeretrograde conduction to the atrium if the atrial pacing pulse did notcapture the atrium. The system determines if 164 the atrial pacing pulsecaptured the atrium. If the system determines that the pacing pulse didnot capture the atrium, then atrial retrograde management is provided165.

In one implementation, the system may detect non-capture if an atrialevoked response is not detected. In this implementation, providingatrial retrograde management may involve delivering an atrial backuppace delivered shortly after the primary atrial pacing pulse.

In another implementation, the system may determine that the atrialpacing pulse did not capture the atrium based on a detected retrogradeP-wave. In this implementation, providing retrograde management mayinvolve delaying a next scheduled atrial pacing pulse until afterexpiration of an atrial effective refractory period as described in moredetail below.

FIG. 1E is a flowchart illustrating in more detail a retrogradeconduction management method in accordance with embodiments of theinvention. In this example, the system sensed for a retrograde P-waveand determines that an atrial pacing pulse did not produce capture ofthe atrium if the retrograde P-wave is sensed. The retrograde P-wave maycause the next scheduled atrial pace to be delivered while the atrialtissue is refractory. The scheduled atrial pace will be ineffectivebecause the atrial tissue will not be able to react to the scheduledatrial pace. The system avoids delivery of atrial pacing while theatrial tissue is refractory, the system delays delivery of the nextscheduled atrial pace until after expiration of an atrial effectiverefractory period (AERP).

In the flowchart of FIG. 1E the system delivers 139 a next scheduledatrial pacing pulse and delivers a ventricular pace if an intrinsicventricular depolarization is not sensed 141 during an AV interval.Following delivery of the ventricular pace or intrinsic ventriculardepolarization, for example, during PVARP, the system senses for 142 aretrograde P-wave. If a retrograde P-wave is not detected 142, thenretrograde management is not necessary for the next cycle and the systemdelivers 139 the next scheduled atrial pulse after an A-A interval hasexpired 167.

If the retrograde P-wave is detected 142, a check is performed todetermine if the time between the retrograde P-wave and the nextscheduled atrial pace is longer than an atrial effective refractoryperiod (AERP). For example, a suitable AERP may vary from patient topatient and may be about 200 to 300 milliseconds. If the time is shorterthan the AERP, the next atrial pacing pulse is rescheduled 149 bydelaying it to occur after the AERP has expired. If the check 145 findsthat the time is longer than the AERP, then the timing of the nextatrial pacing pulse is not changed, and the system delivers the nextatrial pacing pulse as scheduled.

If the next atrial pacing pulse is delayed 149, and there is no atrialsense 144 before that time, then the energy of the delayed atrial pacingpulse may be increased 146 over a previously delivered pacing pulse toensure capture. A check 148 is then performed to see if an atrial evokedresponse is detected after delivery of the high energy atrial pacingpulse 147. This step determines if the current AERP is long enough. Ifthe evoked response 148 to the high energy pace 147 is detected, thenthe AERP is sufficiently long, and the current AERP may be maintained.If there is no evoked response 148 to the high energy atrial pace, thenthe AERP is insufficient in length and is adjusted 165. If there is noevoked response 148 to the high energy atrial pace, then the AERP isinsufficient in length and is adjusted 165. The system paces or sensesthe ventricle 166 and waits 167 for the next A-A interval.

The operation of the retrograde management method described inconnection with the flowchart of FIG. 1E is illustrated in the graphs ofFIGS. 1F and 1G. FIG. 1F illustrates a pacing response graph of apacemaker without backup pacing and no retrograde management. In thegraph of FIG. 1F, an atrial pace 152 is provided, but capture does notoccur. A ventricular pace pulse 158 is delivered after anatrioventricular (AV) delay. The ventricular pace pulse 158 is followedby the PVARP 140. Retrograde conduction occurs, resulting in aretrograde P-wave 153 sensed during the PVARP 140. The PVARP preventsthe retrograde P-wave from initiating an AV interval. However, with noretrograde management as discussed above, the next scheduled atrial pace154 is delivered during the atrial refractory period 170. The atrialpacing pulse 154 is ineffective, setting up another ventricular pacepulse 160 followed by the PVARP 140, and again a retrograde P-wave 155.This process may continue through an ineffective atrial pacing pulse 156and a subsequent ventricular pacing pulse 162, resulting in repeatedineffective atrial paces and loss of AV synchrony.

FIG. 1G illustrates a pacing response graph of a pacemaker with nobackup pacing but having a method of retrograde management in accordancewith embodiments of the invention. In the graph of FIG. 1C, an atrialpulse 172 is provided, but capture does not occur. A ventricular pacepulse 178 is provided after an atrioventricular delay. The ventricularpace pulse 178 is followed by the PVARP 140. Retrograde conductionoccurs, resulting in retrograde P-wave 173 sensed during the PVARP 140.The pacemaker initiates an AERP 170 relative to the sensed retrogradeP-wave 173. Due to the sensed retrograde P-wave 173, the pacemakerdelays an atrial pace 174 for the next cardiac cycle until expiration ofthe AERP 170. Delaying the next scheduled atrial pace 174 until afterexpiration of the AERP 170 prevents the next scheduled atrial pace 174from being delivered while the atrial tissue is refractory due to theretrograde P-wave 173. An evoked response signal 126 may be sensed afterthe atrial pace. AV synchrony and effective atrial pacing are maintainedfor atrial 176 and ventricular 180, 182 pacing pulses during subsequentcardiac cycles.

The capture verification and retrograde management processes describedherein may be utilized in connection with pacing the left and/or rightatria. Various embodiments of the invention involve using the sameelectrode combination for pacing and sensing. Other embodiments involveusing an electrode combination for pacing that is different from theelectrode combination used to sense the cardiac signal following pacingfor capture verification. Employing different electrode combinations forpacing and sensing may enhance cardiac response determination. Further,the same or different electrode combinations may be utilized in sensingfor an evoked response and in sensing for a retrograde P-wave.

The embodiments of the present system illustrated herein are generallydescribed as being implemented in an implantable cardiacpacemaker/defibrillator (PD) that may operate in numerous pacing modesknown in the art. Various types of single and multiple chamberimplantable cardiac defibrillators are known in the art and may be usedin connection with the atrial capture verification methods of thepresent invention. The methods of the present invention may also beimplemented in a variety of implantable or patient-external cardiacrhythm management devices, including dual chamber pacemakers,defibrillators, cardioverters, bi-ventricular pacemakers, cardiacresynchronizers, for example.

Although the present system is described in conjunction with animplantable cardiac defibrillator having a microprocessor-basedarchitecture, it will be understood that the implantable cardiacdefibrillator (or other device) may be implemented in any logic-basedintegrated circuit architecture, if desired.

Referring now to FIG. 2 of the drawings, there is shown a cardiac rhythmmanagement system that may be used to implement capture verification andretrograde management methods of the present invention. The cardiacrhythm management (CRM) system in FIG. 2 includes a PD 200 electricallyand physically coupled to a lead system 202. The housing and/or headerof the PD 200 may incorporate one or more electrodes 208, 209 used toprovide electrical stimulation energy to the heart and to sense cardiacelectrical activity. The PD 200 may utilize all or a portion of the PDhousing as a can electrode 209. The PD 200 may include an indifferentelectrode 208 positioned, for example, on the header or the housing ofthe PD 200. If the PD 200 includes both a can electrode 209 and anindifferent electrode 208, the electrodes 208, 209 typically areelectrically isolated from each other.

The lead system 202 is used to detect electric cardiac signals producedby the heart 201 and to provide electrical energy to the heart 201 undercertain predetermined conditions to treat cardiac arrhythmias. The leadsystem 202 may include one or more electrodes used for pacing, sensing,and/or defibrillation. In the embodiment shown in FIG. 2, the leadsystem 202 includes an intracardiac right ventricular (RV) lead system204, an intracardiac right atrial (RA) lead system 205, an intracardiacleft ventricular (LV) lead system 206, and an extracardiac left atrial(LA) lead system 210. The lead system 202 of FIG. 2 illustrates oneembodiment that may be used in connection with the methodologiesdescribed herein. Other leads and/or electrodes may additionally oralternatively be used.

The lead system 202 may include intracardiac leads 204, 205, 206implanted in a human body with portions of the intracardiac leads 204,205, 206 inserted into a heart 290. The intracardiac leads 204, 205, 206include various electrodes positionable within the heart for sensingelectrical activity of the heart and for delivering electricalstimulation energy to the heart, for example, pacing pulses and/ordefibrillation shocks to treat various arrhythmias of the heart.

As illustrated in FIG. 2, the lead system 202 may include one or moreextracardiac leads 210 having electrodes, e.g., epicardial electrodes,positioned at locations outside the heart for sensing and/or pacing oneor more heart chambers.

The right ventricular lead system 204 illustrated in FIG. 2 includes anSVC-coil 216, an RV-coil 214, an RV-ring electrode 211, and an RV-tipelectrode 212. The right ventricular lead system 204 extends through theright atrium 220 and into the right ventricle 219. In particular, theRV-tip electrode 212, RV-ring electrode 211, and RV-coil electrode 214are positioned at appropriate locations within the right ventricle forsensing and delivering electrical stimulation pulses to the heart. TheSVC-coil 216 is positioned at an appropriate location within the rightatrium chamber of the heart 290 or a major vein leading to the rightatrial chamber of the heart 290.

In one configuration, the RV-tip electrode 212 referenced to the canelectrode 209 may be used to implement unipolar pacing and/or sensing inthe right ventricle. Bipolar pacing and/or sensing in the rightventricle may be implemented using the RV-tip 212 and RV-ring 211electrodes. In yet another configuration, the RV-ring 211 electrode mayoptionally be omitted, and bipolar pacing and/or sensing may beaccomplished using the RV-tip electrode 212 and the RV-coil 214, forexample. The right ventricular lead system 204 may be configured as anintegrated bipolar pace/shock lead. The RV-coil 214 and the SVC-coil 216are defibrillation electrodes.

The left ventricular lead 206 includes an LV distal electrode 213 and anLV proximal electrode 217 located at appropriate locations in or aboutthe left ventricle for pacing and/or sensing the left ventricle. Theleft ventricular lead 206 may be guided into the right atrium of theheart via the superior vena cava. From the right atrium, the leftventricular lead 206 may be deployed into the coronary sinus ostium, theopening of the coronary sinus. The lead 206 may be guided through thecoronary sinus to a coronary vein of the left ventricle. This vein isused as an access pathway for leads to reach the surfaces of the leftventricle that are not directly accessible from the right side of theheart. Lead placement for the left ventricular lead 206 may be achievedvia subclavian vein access and a preformed guiding catheter forinsertion of the LV electrodes 213, 217 adjacent to the left ventricle.

Unipolar pacing and/or sensing in the left ventricle may be implemented,for example, using the LV distal electrode 213 referenced to the canelectrode 209. The LV distal electrode 213 and the LV proximal electrode217 may be used together as bipolar sense and/or pace electrodes for theleft ventricle. The left ventricular lead 206 and the right ventricularlead 204, in conjunction with the PD 200, may be used to provide cardiacresynchronization therapy such that the ventricles of the heart arepaced substantially simultaneously, or in phased sequence, to provideenhanced cardiac pumping efficiency for patients suffering from chronicheart failure.

The right atrial lead 205 includes a RA-tip electrode 256 and an RA-ringelectrode 254 positioned at appropriate locations in the right atriumfor sensing and pacing the right atrium. In one configuration, theRA-tip 256 referenced to the can electrode 209, for example, may be usedto provide unipolar pacing and/or sensing in the right atrium 220. Inanother configuration, the RA-tip electrode 256 and the RA-ringelectrode 254 may be used to effect bipolar pacing and/or sensing.

FIG. 2 illustrates one embodiment of a left atrial lead system 210. Inthis example, the left atrial lead 210 is implemented as an extracardiaclead with an LA distal electrode 218 and LA proximal electrode 215positioned at an appropriate locations outside the heart 201 for sensingand pacing the left atrium. Unipolar pacing and/or sensing of the leftatrium may be accomplished, for example, using the LA distal electrode218 to the can 209 pacing vector. Bipolar pacing and/or sensing of theleft atrium may be accomplished through the use of the LA distalelectrode 218 and the LA proximal electrode 215.

Referring now to FIG. 3, there is shown an embodiment of a cardiacpacemaker/defibrillator 300 suitable for implementing an atrial captureverification and retrograde management methodologies of the presentinvention. FIG. 3 shows a cardiac pacemaker/defibrillator divided intofunctional blocks. It is understood by those skilled in the art thatthere exist many possible configurations in which these functionalblocks can be arranged. The example depicted in FIG. 3 is one possiblefunctional arrangement. Other arrangements are also possible. Forexample, more, fewer or different functional blocks may be used todescribe a cardiac pacemaker/defibrillator suitable for implementing themethodologies of the present invention. In addition, although thecardiac pacemaker/defibrillator 300 depicted in FIG. 3 contemplates theuse of a programmable microprocessor-based logic circuit, other circuitimplementations may be utilized.

The cardiac pacemaker/defibrillator 300 depicted in FIG. 3 includescircuitry for receiving cardiac signals from a heart and deliveringelectrical stimulation energy to the heart in the form of pacing pulsesor defibrillation shocks. In one embodiment, the circuitry of thecardiac pacemaker/defibrillator 300 is encased and hermetically sealedin a housing 301 suitable for implanting in a human body. Power to thecardiac pacemaker/defibrillator 300 is supplied by an electrochemicalbattery 380. A connector block (not shown) is attached to the housing301 of the cardiac pacemaker/defibrillator 300 to allow for the physicaland electrical attachment of the lead system conductors to the circuitryof the cardiac pacemaker/defibrillator 300.

The cardiac pacemaker/defibrillator 300 may be a programmablemicroprocessor-based system, including a control system 320 and a memory370. The memory 370 may store parameters for various pacing,defibrillation, and sensing modes, along with other parameters. Further,the memory 370 may store data indicative of cardiac signals received byother components of the cardiac pacemaker/defibrillator 300. The memory370 may be used, for example, for storing historical EGM and therapydata. The historical data storage may include, for example, dataobtained from long term patient monitoring used for trending or otherdiagnostic purposes. Historical data, as well as other information, maybe transmitted to an external programmer unit 390 as needed or desired.

The control system 320 may cooperate with other components of thecardiac pacemaker/defibrillator 300 to control the operations of thecardiac pacemaker/defibrillator 300. In one example, the cardiacpacemaker/defibrillator 300 may incorporate a sensor for determining thepatient's hemodynamic need. The sensor output may be utilized by thecontrol system 320 to deliver pacing at a rate adapted to the activitylevel of the patient. In some implementations, the cardiacpacemaker/defibrillator 300 may include components of an accelerometerand/or a transthoracic impedance sensor for determining the activitylevel and/or respiration rate of the patient.

The control system 320 depicted in FIG. 3 incorporates a cardiacresponse classification processor 325 for determining cardiac responsesto pacing stimulation in accordance with various embodiments of thepresent invention. The control system 320 may include additionalfunctional components including a pacemaker control circuit 322, anarrhythmia detector 321, and a template processor 324, along with othercomponents for controlling the operations of the cardiacpacemaker/defibrillator 300.

Telemetry circuitry 360 may be implemented to provide communicationsbetween the cardiac pacemaker/defibrillator 300 and an externalprogrammer unit 390. In one embodiment, the telemetry circuitry 360 andthe programmer unit 390 communicate using a wire loop antenna and aradio frequency telemetric link, as is known in the art, to receive andtransmit signals and data between the programmer unit 390 and thetelemetry circuitry 360. In this manner, programming commands and otherinformation may be transferred to the control system 320 of the cardiacpacemaker/defibrillator 300 from the programmer unit 390 during andafter implant. In addition, stored cardiac data pertaining to capturethreshold, capture detection and/or cardiac response classification, forexample, along with other data, may be transferred to the programmerunit 290 from the cardiac pacemaker/defibrillator 300.

In the embodiment of the cardiac pacemaker/defibrillator 300 illustratedin FIG. 3, electrodes RA-tip 256, RA-ring 254, RV-tip 212, RV-ring 211,RV-coil 214, SVC-coil 216, LV distal electrode 213, LV proximalelectrode 217, LA distal electrode 218, indifferent electrode 208, andcan electrode 209 are coupled through a switch matrix 310 to sensingcircuits 331-337.

A right atrial sensing circuit 331 serves to detect and amplifyelectrical signals from the right atrium of the heart. Unipolar sensingmay be implemented, for example, by sensing voltages developed betweenthe RA-tip 256 and the can electrode 209. Outputs from the right atrialsensing circuit are coupled to the control system 320.

A right ventricular sensing circuit 332 serves to detect and amplifyelectrical signals from the right ventricle of the heart. Rightventricular cardiac signals sensed through use of the RV-tip 212electrode are right ventricular near-field signals and are denoted RVrate channel signals. A bipolar RV rate channel signal may be sensed asa voltage developed between the RV-tip 212 and the RV-ring 211.Alternatively, bipolar sensing in the right ventricle may be implementedusing the RV-tip electrode 212 and the RV-coil 214. Unipolar ratechannel sensing in the right ventricle may be implemented, for example,by sensing voltages developed between the RV-tip 212 and the canelectrode 209.

Right ventricular cardiac signals sensed through use of defibrillationelectrodes are far-field signals, also referred to as RV morphology orRV shock channel signals. More particularly, a right ventricular shockchannel signal may be detected as a voltage developed between theRV-coil 214 and the SVC-coil 216. A right ventricular shock channelsignal may also be detected as a voltage developed between the RV-coil214 and the can electrode 209. In another configuration the canelectrode 209 and the SVC-coil electrode 216 may be electrically shortedand a RV shock channel signal may be detected as the voltage developedbetween the RV-coil 214 and the can electrode 209/SVC-coil 216combination.

Left atrial cardiac signals may be sensed through the use of one or moreleft atrial electrodes 215, 218, which may be configured as epicardialelectrodes. A left atrial sensing circuit 335 serves to detect andamplify electrical signals from the left atrium of the heart. Bipolarsensing and/or pacing in the left atrium may be implemented, forexample, using the LA distal electrode 218 and the LA proximal electrode215. Unipolar sensing and/or pacing of the left atrium may beaccomplished, for example, using the vector from the LA distal electrode218 to can electrode 209 or the LA proximal electrode 215 to canelectrode 209.

A left ventricular sensing circuit 336 serves to detect and amplifyelectrical signals from the left ventricle of the heart. Bipolar sensingin the left ventricle may be implemented, for example, by sensingvoltages developed between the LV distal electrode 213 and the LVproximal electrode 217. Unipolar sensing may be implemented, forexample, by sensing voltages developed between the LV distal electrode213 or the LV proximal electrode 217 to the can electrode 209.

Optionally, an LV coil electrode (not shown) may be inserted into thepatient's cardiac vasculature, e.g., the coronary sinus, adjacent theleft heart. Signals detected using combinations of the LV electrodes,213, 217, LV coil electrode (not shown), and/or can electrodes 209 maybe sensed and amplified by the left ventricular sensing circuitry 336.The output of the left ventricular sensing circuit 236 is coupled to thecontrol system 320.

The outputs of the switching matrix 310 may be operated to coupleselected combinations of electrodes 211, 212, 213, 214, 216, 217, 218,254, and 256 to an evoked response sensing circuit 337. The evokedresponse sensing circuit 337 serves to sense and amplify voltagesdeveloped using various combinations of electrodes for cardiac responseclassification in accordance with embodiments of the invention.

In the embodiments described below, various combinations of pacing andsensing electrodes may be utilized in connection with pacing and sensingthe cardiac signal following the pace pulse to classify the cardiacresponse to the pacing pulse. For example, in some embodiments, a firstelectrode combination is used for pacing a heart chamber and a secondelectrode combination is used to sense the cardiac signal followingpacing. In other embodiments, the same electrode combination is used forpacing and sensing. Further, the electrodes used to sense for theretrograde P-wave may be different or the same as the electrodes used tosense for the atrial evoked response.

The pacemaker control circuit 322, in combination with pacing circuitryfor the left atrium, right atrium, left ventricle, and right ventriclemay be implemented to selectively generate and deliver pacing pulses tothe heart using various electrode combinations. The pacing electrodecombinations may be used to effect bipolar or unipolar pacing of theheart chambers as described above.

As described above, bipolar or unipolar pacing pulses may be deliveredto a heart chamber using one of the pacing vectors as described above.The electrical signal following the delivery of the pacing pulses may besensed through various sensing vectors coupled through the switch matrix310 to the cardiac response classification processor 325 and used toclassify the cardiac response to pacing.

The switching matrix 310 may be arranged to provide connections tovarious configurations of pacing and defibrillation electrodes. Theoutputs of the switching matrix 310 may be coupled to an evoked response(ER) sensing circuit 337 that serves to sense and amplify cardiacsignals detected between the selected combinations of electrodes. Thedetected signals are coupled through the ER amplifier 337 to a cardiacresponse classification processor 325. The cardiac responseclassification processor 325 includes circuitry configured to determinethe cardiac response to a pacing stimulation. The presence or absence ofan evoked response may be determined based on the amplitude, peak value,peak timing, and/or other morphological features of the cardiac signalsensed following the pacing pulse in accordance with embodiments of theinvention.

In one implementation, the cardiac pacemaker/defibrillator 300 mayutilize the evoked response channel 337 to sense for the atrial evokedresponse (AER) as described herein. The cardiac pacemaker/defibrillator300 may utilize the right atrial sensing channel 331 to sense forretrograde P-waves in the right atrium. The cardiacpacemaker/defibrillator 300 may utilize the left atrial sensing channel335 to sense for retrograde P-waves in the left atrium.

FIG. 4A is a flowchart further describing methods 400 of capturedetection based on retrograde conduction in accordance with the presentinvention. An atrial pacing pulse 402 is delivered, and a check 404 ismade to detect intrinsic ventricular depolarization. If the check 404finds no ventricular depolarization, a ventricular pacing pulse 406 isdelivered. A PVARP 408 is initiated following the ventricular pacingpulse or the intrinsic ventricular depolarization. After initiatingPVARP 408, the system senses 410 for a retrograde P-wave. If theretrograde P-wave is detected 412, during 413 PVARP, then atrialnon-capture 416 is confirmed. If the retrograde P-wave is not detected412 during 413 PVARP, atrial non-capture 414 is not confirmed.

FIG. 4B is a flowchart of a method 430 of retrograde management inaccordance with the present invention. Atrial pacing pulse 432 isdelivered, and a check 434 is made to detect an atrial evoked response.If the check 434 finds no atrial evoked response, and backup pacing 440is not available, then a sense 442 is done for a retrograde P-wave. If aretrograde P-wave is detected 444, and the next atrial pulse isscheduled 448 after AERP, the next atrial pulse is delivered 446 asscheduled. If the next atrial pace is not scheduled 448 after AERP, thenthe pacing energy is increased 450 and a high energy pacing pulse isdelivered 452 after the AERP. If, at the check 434 for atrial evokedresponse, an evoked response is detected, then capture is confirmed 436.If the atrial evoked response is not detected at check 434, but backuppacing 440 is available, then backup pacing is delivered 438 to theatrium. If a retrograde P-wave is not detected 444, the next atrial pace446 may be delivered as scheduled.

FIG. 4C is a flowchart of a method 460 of capture verification andretrograde management in accordance with the present invention. Atrialpacing pulse 462 is delivered, and a check 464 is made to detect anatrial evoked response 464. If there is a detected atrial evokedresponse 464, then capture is confirmed 492, and no retrogrademanagement 494 is used. If there is no detected atrial evoked response464, then non-capture is suspected 466, and a check for intrinsicventricular depolarization 468 is performed. If the check 468 finds noventricular depolarization, a ventricular pacing pulse 470 is delivered.If the check 468 finds a ventricular depolarization, a PVARP 472 isinitiated without the ventricular pacing pulse 470. After initiatingPVARP 472, a sense 474 is made for a retrograde P-wave. If theretrograde P-wave is detected 476, atrial non-capture 482 is confirmed,and a check 484 is performed to see if the next atrial pace is scheduledafter the AERP. If the check 484 determines that the pace is scheduledafter the AERP, then the next atrial pulse is delivered 486 asscheduled. If the check 484 determines that the pace is not scheduledafter the AERP, then the pacing energy is increased 488 and the higherenergy pulse is delivered 490 after the AERP. If the retrograde P-waveis not detected at 476, atrial non-capture 478 is not confirmed, and noretrograde management 480 is used, so the next atrial pulse is deliveredas scheduled.

A number of the examples presented herein involve block diagramsillustrating functional blocks used for coordinated monitoring,diagnosis and/or therapy functions in accordance with embodiments of thepresent invention. It will be understood by those skilled in the artthat there exist many possible configurations in which these functionalblocks can be arranged and implemented. The examples depicted hereinprovide examples of possible functional arrangements used to implementthe approaches of the invention.

It is understood that the components and functionality depicted in thefigures and described herein can be implemented in hardware, software,or a combination of hardware and software. It is further understood thatthe components and functionality depicted as separate or discreteblocks/elements in the figures in general can be implemented incombination with other components and functionality, and that thedepiction of such components and functionality in individual or integralform is for purposes of clarity of explanation, and not of limitation.

Various modifications and additions can be made to the preferredembodiments discussed hereinabove without departing from the scope ofthe present invention. Accordingly, the scope of the present inventionshould not be limited by the particular embodiments described above, butshould be defined only by the claims set forth below and equivalentsthereof.

1. An implantable cardiac device, comprising: a plurality of implantablecardiac electrodes configured to be electrically coupled to a heart;sensing circuitry configured to sense cardiac signals; a processorconfigured to control delivery of a first pacing pulse to an atriumduring a first cardiac cycle, sense for an atrial evoked responsefollowing delivery of and associated with the first atrial pacing pulse,sense for an intrinsic activation of a ventricle during the firstcardiac cycle, deliver a pacing pulse to the ventricle if the intrinsicventricular activation is not sensed during the first cardiac cycle,sense in the atrium for a retrograde P-wave, the retrograde P-waveresponsive to the ventricular pacing pulse or the intrinsic ventricularactivation, classify the cardiac response to the first atrial pacingpulse as a non-captured response if the retrograde P-wave is detectedand the atrial evoked response is not detected, classify the cardiacresponse to the first atrial pacing pulse as a captured response if theatrial evoked response is detected, and, deliver, during a secondcardiac cycle immediately following the first cardiac cycle, a secondatrial pacing pulse to the atrium, the second atrial pacing pulse havinga scheduled delivery time, but the second atrial pacing pulse beingdelivered at a time that is delayed relative to the scheduled deliverytime if the cardiac response of the first atrial pacing pulse isclassified as a non-captured response and if a time period between thedetected retrograde P-wave and the scheduled delivery time is no greaterthan an atrial effective refractory period (AERP).
 2. The device ofclaim 1, wherein the processor is configured to sense for the retrogradeP during a time interval following sensing intrinsic ventricularactivity or delivery of the ventricular pacing pulse.
 3. The device ofclaim 2, wherein the time interval comprises a post ventricular atrialrefractory period.
 4. The device of claim 2, wherein the time intervalbegins about 100 milliseconds following delivery of the ventricularpacing pulse and ends about 500 milliseconds following delivery of theventricular pacing pulse.
 5. The device of claim 1, wherein theprocessor is further configured to deliver additional atrial pacingpulses during cardiac cycles subsequent to the cardiac cycle, deliveradditional ventricular pacing pulses during the subsequent cardiaccycles, sense in the atrium for retrograde P-waves, the retrogradeP-waves respectively responsive to the additional ventricular pacingpulses, and classify cardiac responses to the additional atrial pacingpulses as non-captured responses if the retrograde P-waves are detected.6. The device of claim 5, wherein the processor is configured to deliveratrial pacing pulses, deliver ventricular pacing pulses, sense in theatrium, and classify the cardiac responses beat-by-beat during a pacingtherapy delivered to a patient.
 7. The device of claim 5, wherein theprocessor is configured to deliver the atrial pacing pulses, deliver theventricular pacing pulses, sense in the atrium, and classify the cardiacresponses during a test to determine a capture threshold of the atrium.8. The device of claim 1, wherein the processor is configured to sensein the atrium for a retrograde P-wave during a post ventricular atrialrefractory period.
 9. The device of claim 1, wherein the processor isfurther configured to deliver additional atrial pacing pulses duringcardiac cycles subsequent to the cardiac cycle, sense for atrial evokedresponses following delivery of the additional atrial pacing pulses,sense in the atrium for retrograde P-waves, the retrograde P-wavesresponsive to ventricular pacing pulses or the intrinsic ventricularactivations during the subsequent cardiac cycles, and classify thecardiac responses to the additional atrial pacing pulses based on thesensed atrial evoked responses and the sensed retrograde P-waves,wherein the processor is configured to deliver the atrial pacing pulses,sense in the atrium, and classify the cardiac responses beat-by-beatduring a pacing therapy delivered to a patient.
 10. The device of claim1, wherein the processor is further configured to deliver additionalatrial pacing pulses during cardiac cycles subsequent to the cardiaccycle, sense for atrial evoked responses following delivery of theadditional atrial pacing pulses, sense in the atrium for retrogradeP-waves, the retrograde P-waves responsive to ventricular pacing pulsesor the intrinsic ventricular activations during the subsequent cardiaccycles, and classify the cardiac responses to the additional atrialpacing pulses based on the sensed atrial evoked responses and the sensedretrograde P-waves, wherein the processor is configured to deliver theatrial pacing pulses, sense in the atrium, and classify the cardiacresponses are performed during a test to determine a capture thresholdof the atrium.
 11. The device of claim 1, wherein the processor isfurther configured to deliver, during a second cardiac cycle immediatelyfollowing the first cardiac cycle, a second atrial pacing pulse to theatrium, the second atrial pacing pulse having an increased energyrelative to the first atrial pacing pulse if the cardiac response of thefirst atrial pacing pulse is classified as a non-captured response. 12.The device of claim 1, wherein the processor is configured to increasethe AERP if the second atrial pacing pulse does not capture the atrium.13. The device of claim 1, wherein the second atrial pacing pulse isdelivered at an increased energy relative to the first atrial pacingpulse if the cardiac response of the first atrial pacing pulse isclassified as a non-captured response.
 14. An implantable cardiacdevice, comprising: a plurality of implantable cardiac electrodesconfigured to be electrically coupled to a heart; sensing circuitryconfigured to sense cardiac signals; circuitry configured to controldelivery of a first pacing pulse to an atrium during a first cardiaccycle, sense for an atrial evoked response following delivery of andassociated with the first atrial pacing pulse, sense for an intrinsicactivation of a ventricle during the first cardiac cycle, deliver apacing pulse to the ventricle if the intrinsic ventricular activation isnot sensed during the first cardiac cycle, sense in the atrium for aretrograde P-wave, the retrograde P-wave responsive to the ventricularpacing pulse or the intrinsic ventricular activation, classify thecardiac response to the first atrial pacing pulse as a non-capturedresponse if the retrograde P-wave is detected and the atrial evokedresponse is not detected, classify the cardiac response to the firstatrial pacing pulse as a captured response if the atrial evoked responseis detected, deliver, during a second cardiac cycle immediatelyfollowing the first cardiac cycle, a next atrial pacing pulse to theatrium, delay the next atrial pacing pulse if the retrograde P-wave isdetected and the next atrial pacing pulse is scheduled to occur beforean atrial effective refractory period (AERP), and delay the next atrialpacing pulse if the cardiac response of the first atrial pacing pulse isclassified as a non-captured response and if a time period between thedetected retrograde P-wave and the scheduled delivery time is no greaterthan the AERP.
 15. The device of claim 14, wherein the processor isconfigured to deliver the next atrial pacing pulse as scheduled if theretrograde P-wave is not detected.
 16. The device of claim 14, whereinthe next atrial pacing pulse is delayed until after the atrial effectiverefractory period.
 17. The device of claim 14, wherein an energy of thenext atrial pacing pulse is increased relative to the first atrialpacing pulse.
 18. The device of claim 17, wherein the processor isconfigured to change the atrial effective refractory period if the nextatrial pacing pulse does not produce an evoked response.
 19. The deviceof claim 17, wherein the processor is configured to leave the atrialeffective refractory period unchanged if the next atrial pacing pulseproduces an evoked response.